The presence of ice on the road is a factor in many traffic accidents thus the availability of continuous information representative of the co-efficient of friction between a tire and a road surface can be of significant benefit to drivers of moving vehicles. A display or audible signal indicating the extent of reduced tire adhesion can advise drivers when road conditions change in a manner that is not visually noticeable.
Related devices for U.S. Pat. No. 2,690,668 to Lucas, U.S. Pat. No. 3,538,742 to Benning, U.S. Pat. No. 4,050,290 to Lonnroth.
In order to accurately measure road friction it is preferable to create slip between the tire and the road surface. One means of creating slip is an accelerating or decelerating force applied to a test wheel aligned with the path of travel. Many devices provide intermittent as opposed to continuous measurement due to the pulsed application of braking. In certain other devices, a velocity differential of the tire circumference in relation to the road surface at the point of contact is created. Vehicles using such methods have inevitable scrubbing of the tire, or there is a sacrifice made in the accuracy of the friction measurement to prolong the tire life. Other devices collect data from the four load-bearing wheels of the automobile however such systems cannot provide continuous accurate measurements unless a braking or accelerating force is applied.
The current invention provides continuous measurement capability while reducing the slippage of the tire to a very low rate since the velocity difference between the contact patch of the tire and the point of contact with the surface being tested is minimal. The current invention provides an acceptable test tire mileage, very little effect on vehicle steering, very little effect upon vehicle maximum traveling speed, and very little effect upon fuel efficiency of the carrier vehicle. Although loose snow, rough roads, and other factors may affect accuracy, the invention provides very good consistency in readings at all speeds.
Devices have previously been provided that incorporate a single test wheel set at an angle of yaw i.e. toe-in or toe-out, to impart a measurable force on a load cell or other electronic instrument. The previous devices have been deficient in suspension, especially with respect to the ‘range of travel’ necessary to operate reliably on rough or potholed roads at the speed of highway traffic. Other devices require more than one wheel, a design that is not readily adapted to lighter vehicles traveling at highway speeds.